The present invention relates to a power steering mechanism, and more particularly, to such a mechanism in which the hydraulically-actuated power assist is mechanically connected to the steering worm.
Power steering mechanisms of the type to which the present invention relates may have many different applications, but are most frequently used in larger vehicles such as trucks for which the required turning force is substantially greater than in automotive uses.
In general, power steering mechanisms of this class comprise an input shaft connected to a worm gear, with a sector gear in engagement with the worm and attached to a pitman arm. The sector gear and pitman arm arrangement translate rotation of the worm gear into steering movement of the steering linkage.
Typically, if the mechanism is a power steering mechanism, rotation of the input shaft actuates a valve arrangement which directs pressurized hydraulic fluid to the power assist device. U.S. Pat. No. 3,273,465 illustrates such a mechanism in which the pressurized fluid is ported to one end of a power cylinder, with a piston rod being attached to the steering linkage. Such an arrangement is relatively complex because of the addition of the power cylinder, the connection to the steering linkage and the necessary fluid conduits between the cylinder and the valving. In addition, such a system requires additional space for the cylinder adjacent the steering linkage and therefore, would not be adaptable to many vehicle designs, or would require a redesign of that portion of the vehicle.
U.S. Pat. No. 3,433,127 illustrates another approach in which the pressurized fluid is communicated through a series of longitudinal ports to the opposite end of the worm gear where the pressurized fluid acts on the area of the ball screw piston, making it easier to turn the screw. While this mechanism has the advantage of being a self-contained unit (no external cylinders, conduits, etc.), it retains the disadvantage of complex valving and porting, and in addition, is large and expensive to manufacture.